We may never agree on what NSFW really means, but without a universal definition, our machines will simply act as conduits for our own opinions.

"I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description ["hard-core pornography"], and perhaps I could never succeed in intelligibly doing so.

But I know it when I see it, and the motion picture involved in this case is not that." -- United States Supreme Court Justice Potter Stewart In 1964, the Supreme Court overturned an obscenity conviction against Nico Jacobellis, a Cleveland theater manager accused of distributing obscene material.

It was the first time such charges were brought against a museum in the US, and the photos in questions -- depictions of gay S&M -- were at the center of a national debate headed by the Republican Party.

The prosecution argued that the exhibition, funded by the National Endowment for the Arts, constituted pornography while the defense defined it as art.

Soon after Jacobellis faced the Supreme Court, the United States experienced a sexual revolution followed by the porn boom of the 1970s and, more recently, the advent of the internet.

Today, anyone with an internet connection can be knee-deep in creampies and pearl necklaces in a matter of seconds.

Big players have been sinking big money into cleaning up the internet for decades.